1. Field of the Invention
The present invention relates to an image sensor. More particularly, the present invention relates an image sensor having an improved light receiving function.
2. Description of the Related Art
In general, image sensors are semiconductor devices for converting optical images into electric signals, and are mainly classified into a CCD (Charge Coupled Device) image sensor and a CMOS (Complementary Metal Oxide Semiconductor) image sensor.
The CMOS image sensor includes a photodiode for detecting light and a logic circuit for converting detected light into electric signals to make them as data. As quantity of light received in the photodiode increases, the photo sensitivity of the image sensor is improved.
To improve the photo sensitivity, either a fill factor, which is a ratio of a photodiode area to the whole area of the image sensor, must be increased, or a photo-gathering technology is used to change the path of light incident onto an area other than the photodiode area such that the light can be gathered in the photodiode.
A representative example of the photo-gathering technology is to make a micro-lens. That is, a convex micro-lens is formed on a top surface of the photodiode using a material having superior light transmittance, thereby refracting the path of incident light in such a manner that a greater amount of light can be transmitted into the photo-diode area.
Hereinafter, a method of manufacturing a conventional CMOS image sensor will be described with reference to the attached drawings.
FIG. 1 is a schematic sectional view illustrating a conventional CMOS image sensor.
As shown in FIG. 1, the conventional CMOS image sensor has a cell area and a scribe area. The cell area includes a semiconductor substrate 11, a metal interconnection 12, an interlayer dielectric layer 13, and a SiN layer 14.
In addition, the scribe area includes the semiconductor substrate 11, the interlayer dielectric layer 13, and the SiN layer 14.
The interlayer dielectric layer 13 includes a USG (undoped silicate glass) layer.
Although not shown in the drawings, red, green and blue color filter layers are formed on the SiN layer 14, a planar layer and a micro-lens are sequentially formed on the color filter layers.
Hereinafter, a process of forming a contact hole of the interlayer dielectric layer 13 and the SiN layer 14 of the CMOS image sensor will be described.
First, after forming the USG layer having a thickness of about 10000 Å and a TEOS (Tetra Ethyl Ortho Silicate) having a thickness of about 4000 Å, a CMP (Chemical Mechanical Polishing) process is performed to reduce the thickness by 4000 Å to form the interlayer dielectric layer.
Then, the SiN layer is formed on the interlayer dielectric layer.
After that, a photoresist film is deposited. The photoresist film is subject to the exposure and development process to form a photoresist pattern form forming a contact hole.
Then, the SiN layer and the interlayer dielectric layer (USG layer) are etched by using the patterned photoresist film as a mask, thereby forming the contact hole.
In addition, the SiN layer and the interlayer dielectric layer (USG layer) are sintered, thereby obtaining final interlayer dielectric layer and SiN layer.
After obtaining the interlayer dielectric layer and SiN layer, the color filter layers are formed.
However, according to the above conventional CMOS image sensor, adhesion force between the USG layer and the SiN layer may be lowered at the scribe area during the sintering process.
Since the cell area is densely packed with metal patterns, etc., adhesion force between the USG layer and the SiN layer may not be lowered at the cell area during the sintering process.
However, the scribe area is prepared in the form of a wide dummy area without including the metal patterns. For this reason, SiN particles may drop onto the USG layer during the sintering process, thereby causing fatal damage to the image sensor after the subsequent process (color filter process) has been completed.